Fresh and salt water fish species are well-known as foods for human consumption. Fish processing operations typically involve a number of steps including gutting the fish, removing the head and tail, removing scales, separating the fish fillets from the backbone, and washing and packaging the separated fillets. Many of these steps are automated, and are performed in large capacity machines. Although different fish species are processed in different manners, this invention is of particular interest for processing fish fillets.
One of the drawbacks of fish fillets is the presence in the fillets of thin or fine fish bones, which are commonly referred to as pin bones. These bones are all that remain of the fish skeleton, the bulk of which has been removed during typical fish meat processing as described above. However, pin bones may be secured firmly in the fish fillet flesh, and thus, when the backbone is separated from the fish fillet, remain in the flesh instead of being removed with the remainder of the backbone. The presence of theses pin bones in the fish fillet makes the fillet more difficult and awkward to eat. During cooking, the flesh becomes easily separable from the pin bones. However, the pin bones are typically very fine and may not be easily noticed by the person eating the fish. Thus, there is a tendency for the pin bones to be taken into the mouth, and swallowed. This can lead to choking, or other discomfort in the event that the sharp pin bone is not removed prior to eating the fish.
In the past, attempts have been made to remove pin bones by various mechanisms. For example, U.S. Pat. No. 2,771,511 relates to a tool and a method for deboning fish. The tool, in essence, comprises a pair of tweezers for gripping and pulling a large number of pin bones from the fish fillet simultaneously. However, the tool is manually operated and awkward to use. An attempt to automate the process was provided in U.S. Pat. No. 4,945,607 which relates to a gripping device which automatically extends, opens and closes the jaws for the purpose of gripping the ends of the pin bones to remove them from the fish fillet. However, each of these devices require a precise positioning of the gripping jaws in order to have the desired effect of removing pin bones.
A departure from the "tweezer" approach is embodied in the inventions described in WO 94/10848 and WO 92/12641 where the pin bones are removed by being nipped or snagged between a rotating cylinder and a counter-pressure device.
In both of these inventions, the counter-pressure devices are pivotally mounted in order to accommodate the pin bones as they pass between the counter-pressure device and the cylinder. During such pivoting, the counter-pressure devices move away from the rotating cylinder, thereby defining a gap. This gap is dynamic in that its magnitude will vary during operation of the devices according to the number, size and position of any snagged bones. The counter-pressure devices are biased to return to a start position corresponding to minimum predetermined gap by a resilient member comprising a coil spring, in WO 92/12641 and pin-mounted O-rings in WO 94/10848.
These devices fail to apply and maintain a minimum pressure and tension to snagged pin bones during their withdrawal from the fish fillet, with the result that the bones are often broken and repeated passes of the devices on the fish fillet are required to fully withdraw the pin bones. Such repeated handling inevitably results in bruising of the flesh and scraping of flesh which must be discarded. This diminishes the value of the fillet and also wastes time.
An object of this invention is to address the above-described problems and to maximize the value of a fish fillet by withdrawing pin bones from the fillet with minimal flesh being scrapped and with virtually no bruising of the fillet.